How do I know if I have blown my Holley powervalve? - Ford Muscle Forums : Ford Muscle Cars Tech Forum
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post #1 of 4 (permalink) Old 03-30-2005, 01:10 PM Thread Starter
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How do I know if I have blown my Holley powervalve?


I have a 750 Vacuum Secondary Holley on a very built 302. The motor backfired a few times through the carb when it was new. I just recently started it after the winter, and noticed

1) Seems to have very strong gas smell,and I see wet butterflies down in carb when motor is shut off
2) Motor is hard to start sometimes when warm - seems to be flooded, if I give it any gas before cranking. Starts only after waiting and gas is not touched.
3) Motor idles very well, no roughness at all
4) Motor pulls great, no issues

Other than the issue of starting when warm, strong gas smell when off, and gas in carb when shut off, no issues.

My question is :

Could I have blow the power valve in the carb during the backfires? What are the symptoms?

thanks for any and all help

65 Sunbeam Tiger
472HP 302
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post #2 of 4 (permalink) Old 03-30-2005, 01:28 PM
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How do I know if I have blown my Holley powervalve?

I have limited knowledge on Holleys, but I had a 650 on my built 302 and experienced the same conditions as you regards to running and strong gas smells. What I did was take the top off the carb and found dirt and metal shavings in the float bowls (I ran the carb for about a month with no fuel filter when I finished the car, I know it was stupid). The rear float was also a little high and I adjusted that as well, since it would leak into the carb after shutdown in the back bores. The car ran great after I did that. I never had the powervalve go, but sounds like you will be checking that.

I'm sure you'll get other responses with more experience, but that's what we're here for!
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post #3 of 4 (permalink) Old 03-30-2005, 02:00 PM
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How do I know if I have blown my Holley powervalve?

My edumacated opinion is - yes, you blew it. Or maybe hurt the gasket. You can confirm buy running the car a bit, then carefully pulling the carb and setting it on a big coffee can. Check it after a short time - if you see a gas drip or wet spot in the front center of the base plate, then it's leaking in the PV area. There is a small hole from the carb base for vacuum to reach the PV chamber. The symptoms you describe also indicate a problem. If it's bad enough to empty the bowl, you need to fix it ASAP.

FWIW - I've had two PV gaskets go bad in a week on a singlel carb lately. However, the PV's are cheap - you can get them at O'Reillys, Advance and Pep Boys so it's just as easy to toss both.

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post #4 of 4 (permalink) Old 03-30-2005, 02:49 PM
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How do I know if I have blown my Holley powervalve?

I'm inclined to think the problem is not the power valve, but it is old gas, heat soak and too high of a float setting, since the engine still idles well.

Wet butterflys is fuel dripping from the boosters, the result of too high a float setting or the fuel getting too hot and boiling; heat soak or old gas. Re-set the float level and run that tank out before you do anything. Get it as low as possible and fill it up with fresh gas and see if the problem goes away. If it doesn't, I'd look into a phenolic spacer under the carb to insulate it from the engine heat.

...nothing worthwhile is ever easy....
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